a) Field of the Invention
The present invention relates generally to coke drums, and more particularly to an apparatus which is used in connection with a drill assembly that is used in the coking drums for removing the coke from the coke drum.
b) Background Art
Coke is commonly made in a petroleum processing facility as follows. The petroleum product goes through a fractionating process where some of the more volatile material is extracted, and the petroleum product that remains is a heavy, more viscous petroleum product which is at about 720° degrees F. when it leaves the fractionator. This is passed through a heater which raises the temperature of the petroleum product to about 930° degrees F., and this petroleum product is directed through a switch valve alternatively into one or the other of two coke drums. When the petroleum product is being directed into the first coke drum, the coke drum is substantially closed. The feeding of the viscous petroleum product is continued until it reaches a level in the first drum which is about 20 feet from the top of the drum. When the first coke drum is filled to this level, then the switch valve is operated to direct the viscous petroleum product into the second coke drum.
With filling of the first drum being completed, steam is directed upwardly through the petroleum product in first the drum to drive off the lower boiling point volatiles which are discharged from an upper coke drum opening and through one or more vents. After a period of time when removal of the lower boiling point volatiles from the coke has been completed, there remains the coke product which is in the form of a porous solid.
The next step is to cool this porous solid coke product, and this is accomplished by passing water upwardly through the coke product that is still in the drum. After this cooling period, a drill head which is attached to a drill stem is lowered into the coke drum through the top central opening in the coke drum. When the drill head reaches the proper operating position, the drilling starts by use of high pressure water jets (e.g. 3,000–4,000 PSI). In accomplishing the drilling process, the drill head is first set so that the high pressure water will be discharged through the pilot jets which are arranged to drill downwardly to form a central hole in the coke material. Then the drill stem is raised to lift the cutting head out of the coke drum, and the setting of the cutting nozzles is changed so that the laterally directed cutting jets will operate. The drill head is moved downwardly again into the coke drum and when it reaches the level of the petroleum product, the other set of water jet nozzles are used to discharge laterally directed water jets to remove the rest of the coke material from the wall of the coke drum. During this time, the bottom closure plate is opened to permit the water with the coke product to be discharged from the bottom of the drum, and from there is carried to another location. With this being completed, the first drum is again filled with the viscous petroleum product, and at the same time the process described above is repeated in the second drum which has now already been filled with the viscous petroleum product.
The system is arranged so that when the drill head is moved up above the level of the coke drum, an automatic interlock operates which prevents the water to be discharged from the nozzles. However, it could occur that this interlock may be disabled or otherwise made inoperative, so that when the drill stem is brought up, the water jets could be discharged outwardly at a high velocity, thus possibly causing damage to various equipment, injuring personnel, or even killing nearby personnel.